In immune baboons, adult Schistosoma mansoni show a decreased rate of oviposition. We propose to examine this phenomenon on the hypothesis that it is a manifestation of the host immune response distinct from concomitant immunity (for which some evidence already exists). The lack of cellular adherence to adult worms in situ suggests antibodies as the mediators of the anti-oviposition effect. We propose first a morphological confirmation of the hypothesis by the study of small worms recovered from immune hosts. We will attempt to dissociate tegumental-bound immunoglobulins from worms and, in parallel with a stuy of baboon anti-schistosome antibodies, to identify their class and subclass characteristics, as well as functional properties such as complement binding or homocytotropicity. Successful isolation of these antibodies will allow their use in either short-term experiments as possible metabolic inhibitors or in longer-term experiments as possible anti-fecundity agents. BIBLIOGRAPHIC REFERENCES: Damian, R.T., Greene, N.D. and Fitzgerald, K.: Schistosomiasis mansoni in baboons. II. Acquisition of immunity to challenge infection after repeated small exposures to Schistosoma mansoni cercariae. Amer. J. Trop. Med. Hyg., 23:78-80, 1974. Kemp, W.M., Greene, N.D. and Damian, R.T.: Sharing of Cercarienhullen Reaktion antigens between Schistosoma mansoni cercariae and adults and uninfected Biomphalaria pfeifferi. Amer. J. Trop. Med. Hyg., 23: 197-202, 1974.